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Thread: Rebar in Footing

  1. #1

    Default Rebar in Footing

    Hi Everyone,

    I totalled up the expected loads for the small "bump-out" I'm adding to the kitchen. To error on the side of caution, I doubled the figure and used that in combination with the load bearing figures for clay. That adds up to a greatly exagerated size of 32" dia footing (I'll be using two).

    As a double check, using the tables for a one story addition and clay soil (R403.1), I need a 12" wide footing. If I take that bearing area over the length of the wall and divide it into two round footings, I get 36" dia (pretty close).

    I'm becoming a big chicken with this work, so while the engineer is sizing the headers I'll have him double check the footing size.

    The question is, is there any recommendations as to placing rebar in the footing? A 6x6 column will be attached to the footing using a J-bolt and Simpson post base. I may have missed it but I didn't seen any requirement about rebar in the IRC for footings, only for foundations.

    Frost depth is 24" so I'll make the footing 30" deep plus an inch or two above ground. I'll be using 2500 psi concrete. Is the J-bolt enough or should there be additional rebar. What size and orientation for rebar within the footing. I did read that rebar should be covered by at least 3" of concrete.


  2. #2


    We rearly use bar in footings around here but what you are discussing would not be considered a footing. Footings in my area are only for weight distribution below the foundation.

    Also around here we have expansive clay which can require a more concentrated load on the soil so upsizing any bearing on the soil is not recomended.

    I'm used to all foundations being engineered but I know most of the country does not require this.

  3. #3


    Guess that expansive clay requires a delicate balance between the building pushing the footing down and the clay pushing it back up!

  4. #4


    Good luck! Sure hope you'd be successful with this project. You just got to find the right materials, dude.

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  5. #5


    First thing you should do is dig down on your existing building you are adding on to. If that existing building is not frost protected then you don't want to frost protect that add on being attached to it. Many older homes were set on top of the ground not frost protected. If you attach a frost protected addition to a nonfrost protected existing building you just created a difference of potential causing the old existing house to heave up when frost enters below the footer but the new addition will stay the same elevation causing the two structures to rip apart where they were joined. Check what you are attaching to and match the existing with the new to keep heave potential equal.

    The IRC does not require rebar re-enforcement unless you are bridging over disturbed dirt such as where a tree was remove. There you need the rebar to bridge over that disturbed dirt. Otherwise the IRC does not require rebar re-enforcement in a dwelling footer. Remember also the IRC rules are minimum buolding standards. It is advised to go a bit better than minimum. Goal is that you know what minimum is so you can make an informed decision how much more than minimum you want to go. Inspectors love to see more than minimum but can only enforce minimum stadards set by the IRC rules.

    The minimum standards is a 12" wide footer if a curtain style continuous footer to support a single story home with light framing and even brick veneer if single story over clay type soil texture. If you are installing a peir then it is required to be 2' square. Now as said before this is minimum most will go with a 16" wide footer being more than minimum just to be safe in their mind again making an informed decision how much more than minimum you want to go.

    If you use a single L bolt as your anchor to a post how are you going to secure that bolt to a post? Most often an angle plate is installed on each side of that post having a stand plate between that post and the concrete. Remember only heart wood and treated is allowed in direct contact with concrete. Advise the separation plate such as the stand plate installed under that post on that footer.

    Are you adding a pole building style structure to a conventional light frame existing building?

    Hope this helps


  6. #6


    I came up with an estimate for the diameter of the footing but let a structural engineer specify the size. I ended up going bigger than his minimum size (think I went 22" dia). I also added three lengths of #4 rebar per footing.

    Existing foundation did not have any frost protection. The engineer said that I need to make sure that a line extended down at 45 degrees from the bottom of the pier toward the house MUST not intersect the existing foundation. I did that plus some more. I was very careful not to disturb the soil at the bottom of the hole. I extended the sonotube 8" above grade and used a 6x6 post base to attach a pressure treated post. I wish I went with steel posts but I let a contractor friend talk me out of it. Boy, I was surprised at the cost of large dia sonotube.

    I guess this is considered a pole addition on a conventional structure. Standard framed and foundation house (with basement). Addition is 3'x14' with shed roof (only one story). Basement is walk out so the bottom of the addition is 9' up.

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